1. Field of the Invention
The present invention relates generally to a steam drying apparatus and, more particularly, to a steam drying apparatus for drying a material to be dried, by exposing the material to a vapor of a processing solution. The present invention also relates to a cleaning apparatus incorporating such a steam drying apparatus. And further the present invention relates to a steam drying process for drying the material to be dried, by exposing the material to the processing solution vapor.
2. Description of the Related Art
A process for manufacturing semiconductor devices includes a step for processing semiconductor substrates with a chemical, then a step for washing them with water, and further a step for drying them.
FIG. 24 is a schematic view of a prior art steam drying apparatus. A steam drying apparatus 100 has a process chamber 101. Above this process chamber 101 is provided a shutter 109 through which a semiconductor substrate wafer 200 comes in and out. Also above the process chamber 101 is provided an exhaust port 330a for discharging a gas out of the process chamber. The process chamber 101 is provided at the bottom with a heating coil 105 through which a water vapor 310 passes. At the bottom of the process chamber 101 is held a processing solution (e.g., isopropyl alcohol IPA) 301. The water vapor 310 gives heat to the processing solution when passing through the heating coil 105, turning itself to a drain 311 to be discharged from the heating coil 105. A cooling coil 106 in which the cooling water 320 flows through is installed on the inside wall surface of the process chamber 101 below the exhaust port 330 located in the upper part of the process chamber 101. In the process chamber 101 is provided an inner tank 102. To the bottom of the inner tank 102 is connected the drain pipe 103. The semiconductor substrate wafer 200 held in the wafer cassette 201 is carried into the inner tank 102 by means of an elevator 108.
Next, operation of the steam drying apparatus will be explained.
A raw processing solution 300 is supplied from a raw solution supply pipe 104 to the bottom section of the process chamber 101 while discharging a gas out of the process chamber 101 through the exhaust port 330. Thus a predetermined quantity of processing solution 301 is reserved at the bottom section of the process chamber 101. The water vapor 310 is supplied into the heating coil 105 and the cooling water 320 is fed to the cooling coil 106. Preparations are completed when the processing solution 301 has reached a predetermined temperature. At this time, the process chamber 101 is filled with a processing solution vapor 302 that has evaporated according to the temperature of the processing solution 301. The processing solution vapor 302 is reduced to liquid by the cooling coil 106, passing along a condensate recovery gutter 107 and then back to the bottom section of the process chamber 101. A vapor line (a vapor-liquid boundary) 302a is formed from the lower part of the cooling coil 106 towards the center, and therefore the processing solution vapor 302 is hard to go outside at the upper part of the vapor line 302a.
Next explained is a procedure for drying process. The shutter 109 is opened. The semiconductor substrate wafer 200 set in the wafer cassette 201 is loaded on the elevator 108. The shutter 109 is closed, and the elevator 108 is lowered to a predetermined position, from which the semiconductor substrate wafer 200 is placed in the inner tank 102. An increased quantity of water vapor 310 is supplied to the heating coil 105, to rapidly heat the processing solution 301, thereby producing a large volume of processing solution vapor 302. The processing solution vapor 302 reaches the semiconductor substrate wafer 200 in the inner tank 102 as illustrated. When the semiconductor substrate wafer 200 is at a normal temperature, the processing solution vapor 302 condenses on the surface of the semiconductor substrate wafer 200. The condensate of the processing solution 304 is substituted by a wet component present on the surface of the semiconductor substrate wafer 200, flowing together with the wet component downwards with a gravity. With the continuance of condensation of the processing solution vapor 302, the temperature of the semiconductor substrate wafer 200 keeps on rising, gradually ceasing the condensation and accordingly beginning to dry the surface of the semiconductor substrate wafer 200. During this period, a used processing solution 305 inclusive of the wet component flows from the inner tank 102 through a drain pipe 103, being discharged outside. The vapor line 302a at this time is formed at a higher position than that in the step of preparations. After the surface of the semiconductor substrate wafter 200 has become nearly dry, the elevator 108 is raised. The shutter 109 is opened, and the semiconductor substrate wafer 200 is taken out of the wafer cassette 201, thus completing the drying process.
When the drying process is carried out in the semiconductor substrate wafer cleaning process, the wet component is ultrapure water, and the processing solution is generally IPA (isopropyl alcohol). Recently, there has been developed a processing solution substituting for the IPA, and there is the possibility that, in a similar manner, drying processes for various applications will be realized.
The prior art steam drying apparatus, being constituted as described above, has the following various problems.
First, in the process in which the semiconductor substrate wafer 200 is lowered as low as the level for drying process as shown in FIG. 24, the process chamber 101 and the inner tank 102 are already full of the processing solution vapor 302, therefore there exists the problem that since vapor condensation on the surface of the semiconductor substrate wafer 200 advances upwards from below, foreign substances are likely to remain at a high percentage on the surface of the semiconductor substrate wafer 200.
Furthermore, at the time of the process the quantity of the water vapor 310 to be supplied to the heating coil 105 is increased for rapid heating of the processing solution 301, to thereby generate a large volume of processing solution vapor 302. The temperature of the processing solution vapor 302, therefore, becomes considerably high above the boiling point, resulting in a deteriorated efficiency of condensation on the surface of the material to be dried.
Furthermore there is such a problem that since the vapor 302 of the processing solution condensed by the cooling coil 106 and recovered returns to the bottom section of the process chamber 101, the thus recovered condensate is repetitively recirculated for reuse as the processing solution 301, resulting in deteriorated processing solution 301 due to the mixing and accumulation of the wet component from the surface of the semiconductor substrate.
Furthermore, there is such a problem that with the generation of the processing solution vapor 302, there occurs much of mists having, as a nucleus, impurities already included in the raw processing solution, resulting in a deteriorated characteristic of the semiconductor substrate wafer 200 due to the impurities holding on its surface.
Furthermore, there is such a problem that since the cooling coil 106 is not enough to recover the processing solution vapor 302, and, as illustrated, one-third of a consumption of the processing solution goes out as the exhaust 330 through the exhaust port 330a, the consumption of the processing solution increases.
Furthermore, there is such a problem that since the cooling coil 106 is located in a high position inside the process chamber 101, a special elevator 108 is required to lower the semiconductor substrate wafer 200 to the processing level, and accordingly the apparatus will become very large in size.
Furthermore, the wet component holding on the surface of the semiconductor substrate wafer 200 enters the processing solution 301, accumulating to deteriorate the processing solution. Therefore, the process chamber, being in most cases made of a high-cost material such as quartz for the purpose of preventing corrosion by acid and alkali components in the wet component, is likely to be broken and moreover spare parts also are expensive.
Furthermore, because the air is included in the processing solution vapor 302 in the process chamber 101, there is a very serious danger of explosion when a flammable chemical such as IPA is used as the processing solution 301.